fix_bytes: loosen blacklist matching requirements
On my Linux machine, paths seen by 2to3 include the build directory. We
switch from an exact to substring match to allow 2to3 to work in more
environments.
$ echo "[extensions]" >> $HGRCPATH
$ echo "mq=" >> $HGRCPATH
$ hg init
$ echo 'base' > base
$ hg ci -Ambase
adding base
$ hg qnew -mmqbase mqbase
$ hg qsave
$ hg qrestore 2
restoring status: hg patches saved state